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September 2006 was cooler and wetter than usual. The mean temperature of 26.6 degrees was one degree lower than the normal. The monthly rainfall of 420.2 millimetres was about 40 percent above normal. The accumulated rainfall since January 1 amounted to 2467.1 millimetres, about 23 percent above the normal of 2007.1 millimetres for the same period.
A southwesterly airstream brought fine and hot weather to Hong Kong on the first two days of the month. Under the influence of an upper air disturbance over the coast of southeastern China, the weather became showery on September 3 and 4. As the upper air disturbance moved west away from Hong Kong, the weather turned mainly fine in the next two days.
A trough of low pressure over southern China moved south across coastal areas on September 7 and brought scattered showers and squally thunderstorms to Hong Kong. The weather remained cloudy with a few showers on the next day. Local weather deteriorated with heavy rain on September 9 when a cold front crossed the south China coast. More than 100 millimetres of rainfall was recorded at Shatin, Tai Po and the western part of Hong Kong Island and Kowloon. Under the influence of the northeast monsoon behind the cold front, it was cooler with some rain in the ensuing three days.
An area of low pressure over the northern part of the South China Sea developed into a tropical depression on September 12. It moved north initially and then took on a west-northwesterly track. The tropical depression weakened into an area of low pressure over coastal waters of western Guangdong the following night. The outer rain band of the tropical depression brought torrential rain to the territory on September 13. Over 200 millimetres of rainfall was recorded in most places of Hong Kong. There were over 30 reports of flooding and 9 reports of landslide. The weather stayed mainly cloudy with a few showers in the following three days.
Weather improved on September 17 as a continental airstream prevailing over southern China. Sunny weather persisted in the next five days. It was windy on September 23 and 24 under the influence of an intense northeast monsoon. A ridge of high pressure brought generally fine weather to southeastern China from September 25 to 29.
After crossing the Philippines, Typhoon Xangsane entered the South China Sea on September 29 and continued to move westward towards Vietnam. The outer cloud bands of Xangsane brought some rain patches to the territory on September 30.
Six tropical cyclones occurred in the western North Pacific and the South China Sea in the month.
Details of the issuance and cancellation of various warnings/signals in the month are summarised in Table 1. Monthly meteorological figures and departures from normal of September are shown in Table 2.
Ends/Wednesday, October 4, 2006
Issued at HKT 15:25
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